As a driving unit of a vehicle, a power unit in which an engine and a transmission are integrated is used. In such a power unit, in addition to the engine and the transmission, a hydraulic clutch configured to cut off and connect power between the engine and the transmission, a working oil supply system configured to supply oil into the hydraulic clutch, a lubrication oil supply system configured to lubricate sliding parts of the engine or the transmission using the oil, or the like, is installed in a power unit case (for example, see Patent Document 1).
FIG. 17 is a view schematically showing a structure of an oil supply system of a general power unit.
Further, reference numeral 201 in FIG. 17 is a crank shaft of an engine E, reference numeral 202 is a main shaft of a transmission M, and reference numerals 203A and 203B are hydraulic clutches disposed at a shaft end of the main shaft 202 and configured to perform a cutting and connecting of power between the engine E and the transmission M.
The power unit shown in FIG. 17 has an oil storage section 205 formed at a bottom section of a power unit case 204, and a working oil pump 206 and a lubrication oil pump 207 that are installed above the oil storage section 205. The working oil pump 206 is configured to supply oil into the hydraulic clutches 203A and 203B. The lubrication oil pump 207 is configured to supply oil into the sliding parts of the engine E, the transmission M, or the like. The working oil pump 206 and the lubrication oil pump 207 have suction sections opened in the oil storage section 205 via a strainer 208, and ejection sides connected to a working oil passage 209 and a lubrication oil passage 210. The working oil passage 209 is connected to hydraulic pressure introduction parts of the hydraulic clutches 203A and 203B, and the oil discharged from the hydraulic clutches 203A and 203B is returned to the oil storage section 205 through a predetermined passage. In addition, the oil supplied into the lubrication oil passage 210 is returned to the oil storage section 205 after lubricating the sliding parts of the engine E, the transmission M, or the like.
In the middle of the working oil passage 209 and the lubrication oil passage 210 of the power unit, relief valves R1 and R2 and oil filters F1 and F2 are individually interposed, and hydraulic pressure detection parts S1 and S2 configured to detect a decrease in pressure of the oil in the oil passages 209 and 210 to a predetermined value or less and output an alarm signal are installed. A controller that receives the alarm signals from the hydraulic pressure detection parts S1 and S2 prompts an alarm to supplement oil to a user by, for example, lighting an alarm lamp in a display panel.
In addition, a power unit in which an engine and a transmission are integrated is used as a driving unit of a vehicle. As such a power unit, a structure configured to pump oil flowing into a specified space section in a power unit case into an oil storage section using a scavenging pump is known (for example, see Patent Document 2).
In the power unit disclosed in Patent Document 2, the inside of the power unit case is partitioned into a low liquid surface chamber (a specified space) in which a liquid surface height of oil is to be lowered and an oil storage section configured to store oil, and the scavenging pump is installed at a position lower than that of the liquid surface height of the oil storage chamber.
A suction passage extending upward from the low liquid surface chamber is connected to a suction section of the scavenging pump, and a strainer is connected to a suction port of the suction passage facing the inside of the low liquid surface chamber. In addition, a shaft part of the scavenging pump is constituted as a common shaft with a shaft part of a lubrication oil pump close thereto, and an end portion of the shaft part is immersed in oil in the oil storage section.